This invention relates to a needle selection device in a circular knitting machine, in particular a hose knitting machine. More specifically, the invention relates to a selection device of the type which comprises a plurality of superimposed selecting levers, which are individually pivoted to a common structure and selectively movable between a position whereat one end thereof is located level with pattern jack butts to interfere therewith and urge the respective pattern jacks into an inoperative or rest position, and a position whereat said end is located at an intermediate level between the jack butts such as not to interfere therewith, the selective movement of the levers being accomplished through program controlled actuator means.
A device of this type is known from French Pat. No. 2,219,264. In this device, the actuator means for the selective movement of the selecting levers comprise electromagnets, each associated with a respective selecting lever at the end of the latter remote from the end intended for interfering with the jack butts, the various electromagnets being selectively energized in accordance with the machine knitting program.
This known device, however, has the disadvantage of being unsuitable for use on small size machines, such as hose knitting machines, because the arrangement of the various electromagnets above the respective levers requires much space. If the dimensions of the electromagnets are reduced for space reasons, the power available would be insufficient to attract the levers, which attraction is to occur, among others, against the bias of return members to permit the levers to return to the rest position upon de-energization of the respective electromagnets.
To obviate this shortcoming, attempts have been made to reduce the attraction distance between each electromagnet and the respective selecting lever. That is, it has been proposed to mechanically displace the individual levers into a position very close to the pole pieces of the respective electromagnets, or even to contact them, and to energize the electromagnets after the levers have reached that position. In practice, the electromagnets have rather been assigned the task of holding levers which have been previously displaced mechanically.
However, that procedure involves the preliminary displacement of all the levers, even those which, in accordance with the knitting program, should not be moved out of their rest positions. These are thus returned to their rest positions because the respective electromagnets are no longer energized to hold them.
The preliminary mechanical displacement is achieved, for example, through pattern jack butts acting on a profile portion of the selecting levers, as disclosed in British Pat. No. 1,481,146 (corresponding to U.S. Pat. No. 3,998,073) and in British Pat. No. 1,445,038, in which latter the selecting levers actually comprise flexible foils secured at one end thereof. The profile portion is followed by a recessed portion, which allows the respective levers to be returned to the rest postion lacking attraction by the associated electromagnets. It will be appreciated, however, that in addition to the need for mechanically urging indifferently all of the butts prior to the selection proper and for providing other complementary means of preliminary displacement, it becomes necessary to widen the individual levers apart such as to produce a sufficient circumferential extension of the profile and recessed portions to allow for the required displacements of the levers during the short time period of passage of the butts. In other words, it is necessary to increase the mass of the levers, which again imposes higher power requirements on the electromagnets, even though they are only energized to hold the levers. Above all, however, a device of that type is not useful for high speed machines, where the time allowed for the various displacements would be not enough unless the circumferential bulk of the levers themselves were further increased.
In the cited British Pat. No. 1,445,038, a solution is also described wherein the individual levers or foils are preliminarily shifted by means of disk cams arranged respectively under the foils and set to rotate synchronously with the needle cylinder. However, the latter solution exhibits serious space problems, especially in height, resulting from the need for superimposing a disk cam and electromagnet for each selecting lever. Moreover, that solution is also unsatisfactory from the standpoint of the knitting operation rate, owing to the sudden release of those foils which are not intended to be held attracted, which release action involves vibrations of the foils themselves before they are brought to their rest positions, a behavior which is further aggravated by the foils being of a flexible nature. Thus, in the instance of high rate knitting, the time available would be insufficient to ensure damping of such vibratory movements.